During the manufacturing process of fish meal, the raw material (fresh anchovy) is cooked and then undergoes a pressing process, obtaining a press liquor from which the suspended solids and the fat fraction (oil fish) are separated by centrifuging, remaining at the end a liquid called stickwater or fish stickwater. Stickwater can also mean the liquid fraction obtained from fish or cephalopods cooking broth (hereinafter fish) in the production process of canned foods or precooked products, which can then be subjected to a freezing or cure process. Fish stickwater mainly contains a large amount of soluble proteins, insoluble solids, vitamins and minerals (including salt), and fat traces with values that vary depending on the species processed. The amount of stickwater produced basically depends on the composition of the raw material and a suitable cooking and pressing process, which can be 20 and 70% of the processed fish in the case of fish meal. The total solids content in this liquid usually varies between 4-9%, with a variable fat content of 0.3-1.0%, depending on the raw material, its freshness, and centrifugal equipment available. The salt content is also variable, although it is common to see concentrations above 1% (w/w), as in the case of the fishmeal process.
What are the uses of stickwater?
Usually during the preparation of fish meal, stickwater undergoes a concentration process from 6-9% of solids to a final varying concentration of 35-45%, depending on the operational variables and additives used in this process. This concentrate is then incorporated into the production flow of fish meal, which is reflected in a higher volume of product made, with an increase of around 25%. As a result, stickwater recovery, in addition to solving an environmental problem, is highly profitable from the economic point of view. Alternatively, concentrated stickwater can be directly spray dried to a 5% level of humidity, in order to be used separately as an important additive of high biological value on CHI specialized food formulation. In general, concentrated stickwater provides among other components a series of nucleotides and genetic material involved in biochemical processes of attractability, immune stimulation and vital energy, as well as free amino acids, vitamins and minerals, where—according to recent research—the unknown growth factor generally attributed to fish meal can be found.
On the other hand, stickwater obtained from the cooking process in the canning and freezing industry is usually derived to effluent treatment systems, where oil with a high degree of oxidation and sludge are usually obtained and then subjected to a dehydration process to recover fish meal of very low quality.
What problems result from the use of stickwater?
Beyond the environmental and economic benefits that entail the use of this subproduct, the concentration process of stickwater, besides condensing the present soluble protein, can concentrate other solid compounds, including salt. By adding this concentrate to fish meal, salt is added at levels that often exceed the standard set by users for this compound (3.5%), lowering the quality of the final product. Depending on the quality of the processed raw material, stickwater concentrate incorporated to fish meal may also carry decomposition products like biogenic amines including histamine, and volatile nitrogenous bases that greatly lower the quality of fishmeal. The problem is further emphasized when the stickwater concentrate is dried directly and the final product achieves salt levels up to 15% (dry basis), making the percentage protein content relatively low (67%), which reduces the competitiveness of the product when compared with fish protein concentrates from other sources that are offered with a protein content greater than 80%.
Generally, the current use of stickwater favors the underutilization of a major source of protein that, when used as a subproduct in the fish meal process, can lower the quality of this product and, if used as a separate consumable, it has low protein contents due to the salt content accumulated during its process.
Is there a technique used for the removal of salt (demineralized) from fish stickwater?
Now in the fishing industry, stickwater plants are evaporators and therefore tend to concentrate the compounds contained in this subproduct, increasing the salt content in the dehydrated concentrates obtained; i.e., no method or technique is applied to remove salt from fish stickwater.
Is there a proprietary technology for the production of hydrolyzed stickwater protein and what are the differences when compared to our proposal?
The invention patent request (ES 2 311 990 T3) for “Product of hydrolyzate marine protein, process for its production and application” discloses the obtaining of marine protein from any source and fish and shellfish species that generally includes subproducts such as stickwater. The method describes how the protein is obtained by separating it through filtering operations (Ultra and Nano), for which ultrafiltration systems with ceramic membranes are used and then nanofiltration systems that allow the removal of a smaller proportion of salt and biogenic amines.
In this regard, there are a number of differences between the above-mentioned patent and our proposal:
The procedure described in said patent registration (item 6 of claims) does not apply, unlike our proposal, an enzymatic hydrolysis process to stickwater and is only limited to filtering operations (Ultra and Nano).
Another substantial difference is that authors of said patent use ultrafiltration systems with ceramic membranes to remove salt from stickwater and then use nanofiltration to remove the salt and biogenic amines. In our case, our technology only involves electrodialysis to remove with greater efficiency the ions comprising sodium chloride and we do not use conventional filtration methods.
Finally, we also found another difference: the filtration systems applied allow part of the protein components of low molecular weight to pass through the filtration membranes and they are lost along with the water and undesirable compounds such as salt, smell and taste components. This results in the loss of protein components with important biological and technological functionality and reduces the process performance.
Instead, our procedure deals first with the demineralization of stickwater by electrical loads (electrodialysis) in order to make sure not to remove any protein component, because they all are larger than the electrodialysis membranes pores, thus ensuring a greatest number and better quality. Subsequently, hydrolysis allows us to reduce the molecular weight of the protein fractions to give them the desired functionality with the best possible performance.